Semiconductor manufacturing apparatus

ABSTRACT

In an atmosphere of processing gas, on a wafer W consisting mainly of silicon, through a planar-array antenna RLSA  60  having a plurality of slits, microwaves are irradiated to generate plasma containing oxygen, or nitrogen, or oxygen and nitrogen and to implement therewith on the surface of the wafer W direct oxidizing, nitriding, or oxy-nitriding to deposit an insulator film  2  of a thickness of 1 nm or less in terms of oxide film. A manufacturing method and apparatus of semiconductors that can successfully regulate film quality of the interface between a silicon substrate and a SiN film and can form SiN film of high quality in a short time can be obtained.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a manufacturing method ofsemiconductors, in particular detail, to a method for forming gateinsulators in MIS (MOS) semiconductor devices, and to a manufacturingmethod of semiconductor devices provided with insulator films such asgate insulators on a surface of a silicon substrate.

[0003] 2. Description of the Related Art

[0004] Recently, as MIS (MOS) semiconductors have been patterned finer,extremely thin gate insulators such as approximately 4 nm or less are indemand. So far, for gate insulator material, silicon oxide films (SiO₂film) have been industrially used that can be obtained by directlyoxidizing a silicon substrate by use of a high temperature furnace ofapproximately 850° C. to 1000° C.

[0005] However, when the SiO₂ layer is 4 μm or less, a leakage current(gate leakage current) flowing the gate insulator increases to causeproblems such as an increase of consumption power or an acceleration ofdeterioration of device property.

[0006] In addition, there is such a problem that during formation of agate electrode, boron contained therein causes alloy spikes in the SiO₂film to reach the silicon substrate to result in deterioration ofsemiconductor device property. As one method for solving such a problem,nitride film (SiN film) is under consideration as the gate insulatormaterial.

[0007] When the SiN films are deposited by use of CVD method, thereoccur many incomplete bonds (dangling bond) at the interface with thesilicon substrate to result in deterioration of device property.Accordingly, in forming the SiN films, it is considered very promisingto directly nitride a silicon substrate by use of plasma. The reason whyto nitride directly is to obtain gate insulators of high quality thatare less in interface states.

[0008] In addition, one reason for using the plasma is to form SiN filmsat low temperatures. In obtaining SiN films by heating to nitride, hightemperatures of 1000° C. or more are necessary. In the process of theheating, dopant is injected into the silicon substrate. The dopantdiffuses differentially to cause deterioration of device property. Suchmethods are disclosed in Japanese Patent Laid-open Application (KOKAI)Nos. SHO 55-134937 and SHO 59-4059.

[0009] However, in the case of depositing SiN layers with the plasma,the following problems have been pointed out. That is, ions in theplasma are accelerated by a plasma sheath voltage to bombard the siliconsubstrate with high energy, thereby so-called plasma damage occurs atinterfaces of the silicon substrate or on the silicon substrate todeteriorate the device property.

[0010] To this end, a microwave plasma device is disclosed that isprovided with a planar-array antenna that is low in electron temperatureand has a lot of slits causing less plasma damage.

[0011] (Ultra Clean Technology Vol.10 Supplement 1, p.32, 1998u,published by Ultra Clean Society).

[0012] In this plasma device, the electron temperature is approximately1 eV or less and the plasma sheath voltage also is several volts orless. Thus, compared with existing plasma of which plasma sheath voltageis approximately 50 V, the plasma damage can be largely reduced.

[0013] However, even when silicon nitride is formed with this plasmadevice, in the case of forming SiN films by use of direct nitridingmethod, there is the following problem. That is, in order to obtaininterfaces of good quality of less dangling bond defects by dominantlydistributing oxygen only at the interfaces of the silicon substrate,there is a difficulty in regulating film quality at the interfaces withthe silicon substrate.

[0014] In addition, in employing this plasma device to nitride, nitrogenatoms must diffuse into the silicon substrate to proceed nitriding. Thatis a slow process to require a long time to give prescribed processingto an object being processed. Accordingly, the objects can not beprocessed much per unit period to cause difficulties in industrialapplication. In forming SiN films of a thickness of for instance 4 nm,even under the best adjusted plasma conditions of such as pressure andmicrowave power, it takes approximately 5 min or more to process.Accordingly, throughput is much lower than that required from aviewpoint of mass-production, for instance 1 min per one piece of theobject.

SUMMARY OF THE INVENTION

[0015] The present invention is made to solve the aforementionedproblems. That is, an object of the present invention is to provide amethod and an apparatus for manufacturing semiconductors that cansuccessfully regulate film quality at the interfaces between siliconsubstrates and SiN films.

[0016] The other object of the present invention is to provide a methodand an apparatus for manufacturing semiconductors that can form a SiNfilm of high quality in a short time.

[0017] To the above ends, a manufacturing method of semiconductors ofthe present invention is characterized in implementing the invention inthe following manner. That is, in an atmosphere of processing gas,microwaves are irradiated through a planar-array antenna having aplurality of slits on an object to be processed comprising silicon togenerate plasma containing oxygen, or nitrogen, or oxygen and nitrogen.With the plasma, direct oxidation, nitriding, or oxynitriding isimplemented on a surface of the object to form an insulator film of athickness of 1 nm or less (in terms of silicon oxide film).

[0018] In the present manufacturing method, a thickness of insulatorfilm is 1 nm or less. Accordingly, the nitriding of the siliconsubstrate is not due to diffusion but due mainly to a reaction processbetween nitrogen atoms or oxygen atoms or nitrogen and oxygen atomsgenerated by the plasma and the surface of silicon substrate. As aresult of this, a nitriding rate of such short as approximately 30 seccan be obtained.

[0019] On the thin insulator film that is obtained by implementing thedirect nitriding or oxidizing or oxy-nitriding, the rest of theinsulator film is deposited by use of CVD method. In this case, since adeposition rate of 3 nm/min or more can be attained relatively easily,even an insulator film of a total film thickness of 4 nm can be formedin less than two min.

[0020] In addition, in the present manufacturing method, a process forforming, due to direct nitriding or oxidizing or oxy-nitriding, aninsulator film of good quality at an interface with the siliconsubstrate and a process for forming thereon, due to CVD method, the restof the insulator film can be independently implemented. Accordingly,compared with the case where all process is implemented by directnitriding only or CVD method only to form an insulator film, the filmquality at the interface with the silicon substrate can be improved inregulation to result in an insulator film of better quality.

[0021] In the present manufacturing method, for the processing gases, agas containing for instance N₂ or N₂O or NO or NH₃, can be cited. Theprocessing gas can contain rare gas such as argon or the like.

[0022] Another manufacturing method of semiconductors of the presentinvention comprises a step of forming a first insulator film and a stepof forming thereon a second insulator film. Here, the step of formingthe first insulator is carried out in the following manner. That is, inan atmosphere of a processing gas, on an object to be processedcomprising silicon, through a planar-array antenna having a plurality ofslits, microwaves are irradiated to generate plasma containing oxygen,or nitrogen, or oxygen and nitrogen. With the plasma, direct oxidizing,nitriding, or oxy-nitriding is implemented to form the first insulatorfilm.

[0023] In the aforementioned manufacturing method, the second insulatorfilm can be an insulator film comprising for instance silicon nitride.

[0024] The process of forming the second insulator film may beimplemented by use of CVD method, or by use of plasma irradiation.

[0025] Plasma containing for instance N₂ or NH₃ and monosilane ordichlorosilane or trichlorosilane is supplied to form the secondinsulator film.

[0026] According to the present method, in an atmosphere of a processinggas, on an object to be processed consisting mainly of silicon,microwaves are irradiated through a planar-array antenna having aplurality of slits, so-called RLSA (Radial Line Slot Antenna) antenna.Thereby, the plasma is directly supplied on the silicon substrate toform a SiN insulator film. Accordingly, film quality at the interfacewith SiN insulator film formed on a surface of the silicon substrate canbe successfully regulated.

[0027] Furthermore, according to another manufacturing method of thepresent invention, on a first insulator film formed by use of so-calledRLSA antenna, all the second insulator film can be formed by irradiationof the plasma of low damage. As a result of this, a SiN film of highquality can be formed. In particular, when the second insulator film isformed by use of the CVD method, the insulator film can be deposited ina short time to result in formation of a SiN film of high equality in ashort time.

[0028] In addition, in a silicon semiconductor device, so far, as a gateinsulator, silicon oxide film (SiO₂ film) has been used. However, when athickness of SiO₂ film is made thinner than 60 angstroms that is athickness being employed now, there is a lower limit at 40 angstroms.When tried to make thinner than this, a leakage current becomes largerto result in larger power consumption. This is impractical.

[0029] Therefore, a silicon nitride film (SiN film) that does not causea large leakage current when thinning down to approximate 40 angstromsis being considered to use as a gate insulator.

[0030] For instance, Japanese Patent Laid-open Application (KOKAI) Nos.HEI 5-36899 and HEI 9-50996 disclose an example of stacking a siliconnitride film due to thermal nitriding and silicon nitride film due tovapor phase growth method. In an example disclosed in HEI 5-36899,polycrystalline silicon is patterned in a prescribed shape to form anelectrode, followed by fast thermal nitriding at 850° C. for 60 sec withan annealing furnace to form a silicon nitride film of a film thicknessof approximate several nm on a surface of the electrode due to thermalnitriding. On the surface of this silicon nitride film, a siliconnitride film of approximately 4 nm is deposited due to low-pressurevapor phase growth method.

[0031] In Japanese Patent Laid-open Application (KOKAI) No. HEI 6-61470,an example employing a silicon oxynitride film is disclosed. In thisexample, silicon oxide film is annealed in an atmosphere of NH₃ at 900to 1000° C. for approximately 10 min to 1 hour to form siliconoxynitride film.

[0032] Furthermore, in Japanese Patent Laid-open Application (KOKAI) No.HEI 10-178159, an example of a combination of three layers of siliconoxynitride film, silicon nitride film, and silicon oxynitride film isdisclosed. In this example, silicon oxynitride film is formed in thefollowing way. In a low pressure CVD device, from monosilane and nitrousoxide, high temperature silicon oxide film is formed under conditions ofa pressure of approximately 50 Pa and a temperature of 700 to 850° C.Then, at a temperature of 700 to 850° C., nitrous oxide is introduced totransform the high temperature silicon oxide film to silicon oxynitridefilm. On the other hand, the silicon nitride film is formed in a lowpressure CVD device from dichlorosilane and ammonia at a temperature of700 to 850° C.

[0033] However, silicon nitride film due to thermal nitriding has a lotof dangling bonds (free species) and is poor in electrical properties.Silicon nitride film (silicon nitride film) due to low-pressure vaporphase growth method also is poor in electrical properties. In addition,silicon oxynitride film takes a long time to form.

[0034] The present inventors used high-density plasma to generate plasmafrom a mixture of argon gas and nitrogen gas and hydrogen gas to formtherewith SiN film by nitriding a surface of a silicon substrate.Although SiN film of excellent electrical property can be obtained bythis means, there is a disadvantage that SiN film can not be formed witha high rate.

[0035] The present invention is made under such circumstances. An objectis to provide a method for manufacturing semiconductor devices providedwith an insulator film of excellent electrical property and of higherdeposition rate.

[0036] A method for producing semiconductor devices of the presentinvention comprises a step of forming a first silicon nitride film and astep of forming a second silicon nitride film of larger deposition ratethan that of the first silicon nitride film. Here, the first siliconnitride film is formed by nitriding a surface of a silicon substratewith plasma. The plasma is obtained from a gas mixture containing raregas and nitrogen and hydrogen or rare gas and ammonia but not siliconand containing 50% and more and 99% or less of rare gas. The secondsilicon nitride film is formed on the surface of the first siliconnitride film with plasma, the plasma being obtained from a gas mixturecontaining rare gas and nitrogen and silicon and containing 50% or moreand 99% or less of rare gas. At this time, it is preferable to generatethe plasma with high frequency power of 300 MHz or more and 2500 MHz orless.

[0037] In a manufacturing method of semiconductor devices of the presentinvention, insulator film formed at the interface of a silicon substrateis silicon oxide film. The silicon oxide film may be formed by oxidizinga surface of the silicon substrate with plasma or without plasma, theplasma being obtained from a gas mixture containing rare gas and oxygenbut not silicon and containing 50% or more and 99% or less of rare gas.Further, an insulator film formed at the interface of the siliconsubstrate may be silicon oxynitride film.

BRIEF DESCRIPTION OF DRAWINGS

[0038]FIG. 1 is a vertical sectional view of a semiconductor devicemanufactured due to a manufacturing method of semiconductors of thepresent invention.

[0039]FIG. 2 is a schematic diagram showing a manufacturing apparatus ofsemiconductors where a manufacturing method of semiconductors of thepresent invention is implemented.

[0040]FIG. 3 is a vertical sectional view of a RLSA plasma processingunit used in the present manufacturing method.

[0041]FIG. 4 is a plan view of a RLSA used in a manufacturing apparatusof semiconductors of the present invention.

[0042]FIG. 5 is a diagrammatic vertical sectional view of a CVDprocessing unit that is used in the present manufacturing method.

[0043]FIG. 6 is a diagram showing a flow chart of a process for forminggate insulator in the method of the present invention.

[0044]FIG. 7 is a diagram showing the details of formation of gateinsulator due to the present method.

[0045]FIG. 8 is a diagram showing comparison between various depositionconditions and quality performance of gate insulators obtained under thevarious deposition conditions.

[0046]FIG. 9 is a diagram showing relationship between deposition timeand film thickness in various deposition methods.

[0047]FIG. 10 is a diagram showing relationship between deposition timeand film thickness in the present manufacturing method.

[0048]FIG. 11 is a characteristic diagram showing relationship betweenprocessing time and film thickness.

[0049]FIG. 12 is a characteristic diagram showing relationship betweenprocessing time and film thickness.

[0050]FIG. 13 is a characteristic diagram showing relationship betweencapacitance and gate voltage.

[0051]FIG. 14 is a characteristic diagram showing relationship betweenamount of Xe gas and electrical property.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0052] (A First Mode of Implementation)

[0053] In the following, one mode of implementation of the presentinvention will be explained.

[0054] First, an example of a structure of a semiconductor device thatis manufactured due to a manufacturing method of semiconductors of thepresent invention will be explained with a semiconductor device providedwith gate insulator as insulator film as an example with reference toFIG. 1.

[0055] In FIG. 1 A, reference numerals 1, 11, 2 and 13 denote a siliconsubstrate, a field oxide film, a gate insulator and a gate electrode,respectively. The present invention is characterized in a gate insulator2. The gate insulator 2, as shown in FIG. 1 B, is constituted of a firstinsulator film 21 of a thickness of for instance approximately 1 nm anda second film 22 having a thickness of for instance approximately 3 nm.The first insulator film 21 is an insulator film of high quality formedat the interface with a silicon substrate. The second film 22 is formedon an upper surface of the first insulator film 21

[0056] In this instance, a first film 21 of high quality is a firstsilicon oxynitride film (hereinafter refers to as “SiON film”) that isformed by implementing direct oxidizing, nitriding, or oxy-nitridingwith plasma on a surface of an object to be processed. Here, microwavesare irradiated, in an atmosphere of processing gas, on the objectconsisting mainly of silicon, through a planar-array antenna memberhaving a plurality of slits to generate plasma containing oxygen, ornitrogen, or oxygen and nitrogen.

[0057] A second film 22 of which deposition rate is larger than that ofthe first film 21 is formed by forming a second insulator film on thefirst insulator film.

[0058] Next, how to form such a gate insulator 2 will be explained.

[0059]FIG. 2 is a schematic diagram showing an entire configuration of amanufacturing apparatus 30 of semiconductors with which a manufacturingmethod of semiconductors of the present invention is implemented.

[0060] As shown in FIG. 2, at an approximate center of the manufacturingapparatus 30, a transportation chamber 31 is disposed. In addition, soas to surround the circumference of the transportation chamber 31, aplasma processing unit 32, a CVD processing unit 33, two load lock units34 and 35 and a heating unit 36 are disposed.

[0061] Beside the load lock units 34 and 35, a preparatory cooling unit45 and a cooling unit 46 are disposed, respectively.

[0062] Inside of the transportation chamber 31, transporting arms 37 and38 are disposed, with these arms 37 and 38 wafers being transported fromand to each of the aforementioned respective units 32 through 36.

[0063] At this side of the load lock units 34 and 35 in the figure,loader arms 41 and 42 are disposed. These loader arms 41 and 42 get inand out wafers to and from four cassettes disposed on a cassette stage43 disposed at the further this side in the figure.

[0064] The CVD processing unit 33 in FIG. 2 can be replaced by a plasmaprocessing unit that is identical with the plasma processing unit 32,two plasma processing units being able to set.

[0065] Further, both of these units for plasma processing 32 and CVDprocessing 33 can be replaced by a single chamber unit for plasmaenhanced CVD processing. In the place of the plasma processing unit 32or the CVD processing unit 33, one or two single chamber plasma enhancedCVD processing units can be set. When plasma processing beingimplemented with two units, after SiON film is directly formed in theprocessing unit 32, a method for carrying out CVD to deposit a plasmaSiN film may be implemented at the processing unit 33. Instead, twoprocessing units 32 and 33 can be operated in parallel to directly formSiON film and to form SiN-CVD film. Or, the processing units 32 and 33can be operated in parallel to directly form SiON film, thereafterSiN-CVD film being formed with a separate unit.

[0066]FIG. 3 is a vertical sectional view of a unit for plasmaprocessing 32 being used for deposition of gate insulator 2.

[0067] Reference numeral 50 denotes a vacuum chamber composed of forinstance aluminum. On an upper surface of the vacuum chamber 50, anopening 51 larger than a substrate such as a wafer W is formed, a flatcylindrical gas supplying chamber 54 constituted of dielectrics such assilicon nitride being disposed so as to clog the opening 51. At thelower surface of the gas supplying chamber 54, a lot of gas supplyingholes 55 are disposed, gas introduced into the gas supplying chamber 54being supplied in shower into the vacuum chamber 50 through the gassupplying holes 55.

[0068] Outside of the gas supplying chamber 54, through a radial lineslot antenna (hereinafter refers to as “RLSA”) 60 composed of forinstance copper plate, a waveguide 63 is disposed, the waveguide 63constituting a high frequency power supply portion and being connectedto a microwave power supply 61 that generates for instance a microwaveof 2.45 GHZ. A flat and circular waveguide 63A, a cylindrical waveguide63B, a coaxial waveguide converter 63C and a square waveguide 63D arecombined to constitute the waveguide 63. The flat and circular waveguide63A is connected to a lower rim of the RLSA 60. One end of thecylindrical waveguide 63B is connected to an upper surface of thecircular waveguide 63A. The coaxial waveguide converter 63C is connectedto an upper surface of the cylindrical waveguide 63B. The squarewaveguide 63D of which one end is perpendicularly connected to a sidesurface of the coaxial waveguide converter 63C and the other end thereofis connected to the microwave power supply 61.

[0069] In the present invention, a high frequency region includes UHFand microwaves. High frequency power supplied from the high frequencypower supply is in the range of 300 MHz or more and 2500 MHz or lessincluding UHF of 300 MHz or more and microwaves of 1 GHz or more. Plasmabeing generated by these high frequency powers is called high frequencyplasma, here. Inside of the cylindrical wave guide 63B, one end of anaxis 62 consisting of conductive material is connected to an approximatecenter of an upper surface of the RLSA 60 and the other end is coaxiallydisposed to connect to an upper surface of the cylindrical waveguide63B. Thereby the waveguide 63B is constituted to be a coaxial waveguide.

[0070] On a sidewall of an upper side of the vacuum chamber 50, atsixteen positions equally disposed along for instance a circumferencedirection thereof, gas supplying pipes 72 are disposed. From the gassupplying pipes 72, gas including rare gas and N is uniformly suppliedin the neighborhood of a plasma area P of the vacuum chamber 50.

[0071] In the vacuum chamber 50, facing the gas supplying chamber 54, asusceptor 52 of a wafer W is disposed. The susceptor 52 has a built-intemperature regulator that is not shown in the figure, thereby thesusceptor 52 functioning as a heat plate. In addition, to the bottomsurface of the vacuum chamber 50, one end of an exhaust pipe 53 isconnected, the other end of the exhaust pipe 53 being connected to avacuum pump 55.

[0072]FIG. 4 is a plan view of a RLSA 60 being used in a manufacturingapparatus of semiconductors of the present invention.

[0073] As shown in FIG. 4, the RLSA 60 has a plurality of slots 60 a, 60a, - - - on the surface thereof disposed concentrically. Each slot 60 ais a penetrated groove of approximate rectangle, the respective adjacentslots being disposed orthogonal to each other to form an approximatealphabetical “T” character. The length and spacing of the slots 60 a aredetermined according to wavelength of microwaves generated by themicrowave power supply 61. FIG. 5 is a vertical sectional view showingdiagrammatically a CVD processing unit 33 being used in the presentmanufacturing.

[0074] As shown in FIG. 5, a processing chamber 82 of a CVD processingunit 33 is constituted in an air-tight structure of for instancealuminum or the like. Though omitted in FIG. 5, in a processing chamber82 there are provided with a heating unit and a cooling unit.

[0075] In the processing chamber 82, at the upper center thereof, a gassupplying tube 83 is connected to introduce gas, the inside of theprocessing chamber 82 being communicated with that of the gas supplyingtube 83. The gas supplying tube 83 is connected to a gas supply 84. Gasis supplied from the gas supply 84 to the gas supplying tube 83 and thegas is introduced into a processing chamber 82 through the gas supplyingtube 83. For this gas, various kinds of gases that can be raw materialof thin film can be used, and as demands arise, inert gas can be used asa carrier gas.

[0076] At the lower portion of the processing chamber 82, an exhaustpipe 85 for exhausting gas in the processing chamber 82 is connected,the exhaust pipe 85 being connected to an exhausting means consisting ofa vacuum pump or the like that is not shown in the figure. By thisexhausting means, gas in the processing chamber 82 is evacuated from thegas exhaust pipe 85 to set the inside of the processing chamber 82 at adesired pressure.

[0077] In addition, at the lower portion of the processing chamber 82, asusceptor 87 for disposing a wafer W thereon is disposed.

[0078] In the present mode of implementation, with an electrostaticchuck of identical diameter with the wafer W but not shown in thefigure, the wafer W is disposed on the susceptor 87. The susceptor 87has a built-in heating means that is not shown in the figure, a surfaceto be processed of the wafer W that is disposed on the susceptor 87being regulated to a desired temperature.

[0079] The size of the susceptor 87 is one that can accept a wafer W ofsuch large size as 300 mm. As demands arise, the wafer W placed on thesusceptor 87 can be rotated.

[0080] By having a susceptor 87 such large built-in, a wafer w of alarge diameter of 300 mm can be processed, resulting in high yield andless expensive cost ensuing therefrom.

[0081] In FIG. 5, on a sidewall of the processing chamber 82 at theright side of the susceptor 87, an opening 82 a for getting in and out awafer W is disposed. The opening 82 a is opened and closed by moving agate valve 98 up and down in the figure. In FIG. 5, at the further rightside of the gate valve 98, an arm for transporting a wafer W (not shownin the figure) is disposed adjacently. The transporting arm goes in andout the processing chamber 82 through the opening 82 a to dispose thewafer W on the susceptor 87 or take out the processed wafer W out of theprocessing chamber 82. Above the susceptor 87, a shower head 88 isdisposed to shower. The shower head 88 separates a space between thesusceptor 87 and the gas supplying tube 83 and is made of for instancealuminum or the like.

[0082] The shower head 88 is structured for a gas outlet 83 a of the gassupplying tube 83 to locate at the upper center thereof, gas suppliedinto the processing chamber 82 as it is being introduced into the showerhead 88 disposed inside of the processing chamber 82.

[0083] Next, how to form an insulator film consisting of a gateinsulator 2 on a wafer W with the above apparatus will be explained.

[0084]FIG. 6 is a flow chart showing a flow of the respective steps ofthe present method.

[0085] First, in the preceding step, a field oxide film 11 is formed ona surface of the wafer W.

[0086] Then, a gate valve (not shown in the figure) disposed on asidewall of a vacuum chamber 50 is opened to dispose the wafer W on thesusceptor 52 with transporting arms 37 and 38. The wafer W is thesilicon substrate 1 on the surface thereof the field oxide film 11 isformed.

[0087] Subsequently, after the gate valve is closed to seal the inside,by use of a vacuum pump 55, an inner atmosphere is evacuated through anexhaust pipe 53 to be a prescribed degree of vacuum and maintained atthe prescribed pressure. On the other hand, with a microwave powersupply 56, microwaves of for instance 2.45 GHz (3 kW) are generated. Themicrowaves are guided by a waveguide 51 through a RLSA 60 and a gassupplying chamber 54 into the vacuum chamber 50, thereby in a plasmaarea P at the upper side of the inside of the vacuum chamber 50 highfrequency plasma being generated.

[0088] Here, the microwaves propagate in a square waveguide 63D insquare mode, being converted from the square mode to a circular mode ata coaxial waveguide converter 63C, propagating in the circular coaxialwaveguide 63B in circular mode, further propagating in a state expandedat the circular waveguide 63A, being radiated from slots 60 a of theRLSA 60, going through the gas supplying chamber 54 to be led into thevacuum chamber 50. At this time, due to use of the microwaves, higherdensity plasma is generated, and due to radiation of the microwaves froma lot of slots 60 a of the RLSA 60, the plasma becomes denser.

[0089] Then, while regulating the temperature of the susceptor 52 toheat the wafer W at for instance 400° C., Xe gas, N₂ gas, H₂ gas and O₂gas that are a first gas are introduced from a gas supplying tube 72with the flow rates of 500 sccm, 25 sccm, 15 sccm and 1.0 sccm,respectively, to implement a first step.

[0090] In this step, the introduced gas is activated (being convertedinto plasma) by plasma flow generated at the vacuum chamber 3. With theplasma, as shown in FIG. 7A, a surface of the silicon substrate 1 isconverted to oxynitride to form a first insulator film (SiON film) 21.Thus, processing of nitriding is implemented for 30 sec for instance toform the first insulator film (SiON film) 21 of a thickness of 1 nm.

[0091] Next, the gate valve is opened to proceed the transporting arms37 and 38 into the vacuum chamber 50 to receive a wafer W on thesusceptor 52. The transporting arms 37 and 38, after taking out thewafer W from the plasma processing unit 32, set it on the susceptor 87in the adjacent CVD processing unit 33.

[0092] Next, in the CVD processing unit 33, the wafer W is exposed toCVD processing, thereby a second insulator film being formed on thepreviously formed first insulator film.

[0093] That is, in the vacuum chamber 3, under conditions of a wafertemperature of for instance 400° C. and a processing pressure of forinstance from 50 mTorr to 1 Torr, the second gas is introduced into thechamber 82 to implement the second step.

[0094] In specific, from the gas supply 84, a gas containing Si such asSiH₄ gas is introduced at a flow rate of for instance 15 sccm. At thesame time, from the gas supplying tube 83, Xe gas and N₂ gas areintroduced at the flow rates of 500 sccm and 20 sccm, respectively.

[0095] In this step, the introduced second gas is deposited on the waferW to increase film thickness in a relatively short time. Thus, as shownin FIG. 7B, on the surface of the first insulator film (SiON film) 21,the second insulator film (SiN film) 22 is formed. The SiN film 22,being formed at the deposition rate of for instance 4 nm/min, isprocessed for 30 sec for instance to form the second insulator film (SiNfilm) 22 of a thickness of 2 nm. Thus, in the course of total 30 secprocessing, a gate insulator 2 of a thickness of 4 nm is formed.

[0096] In the aforementioned first step, in depositing the firstinsulator film, in an atmosphere of the processing gas, on the wafer Wconsisting mainly of silicon, microwaves are irradiated through aplanar-array antenna (RLSA) having a plurality of slits. Thereby, plasmacontaining oxygen, or nitrogen, or oxygen and nitrogen is formed. Withthis plasma, direct oxidizing, nitriding, or oxy-nitriding isimplemented on the surface of the object to be processed, resulting inhigh quality and successful regulation of film quality.

[0097] That is, quality of the first insulator film is such high asshown in FIG. 8.

[0098] As shown in FIG. 8, according to the manufacturing method ofsemiconductors of the present invention, low level interface statesidentical with those of thermal oxide film can be secured, andinsulation resistance of the gate insulator and alloy spike of boron inthe gate electrode can be reduced.

[0099] By contrast, in the SiN films due to direct nitriding and CVDmethod, the interface states increases compared with the thermal oxidefilm. In this case, carriers disperse largely at the interface to lowera drive current of a transistor.

[0100] The reason why the first insulator film formed due to the abovemethod is high in quality is considered as follows.

[0101] That is, in the present manufacturing method, at the interfacewith a silicon substrate, both of nitrogen atoms and oxygen atomsefficiently terminates bonding of silicon atoms to cause less danglingbonds. In addition, as to the insulation resistance and alloy spike ofthe gate insulator, the CVD-SiN film works effectively. As a result ofthis, in the present manufacturing method, advantages of the directoxynitride SiON film and the CVD-SiN film can be successfully extracted.

[0102] On the contrary, in forming the interface with SiN alone, it isconsidered that termination of the dangling bonds are incomplete toresult in an increase of the interface states.

[0103] By implementing the above second step, the second insulator filmformed on the first insulator film can be deposited in a short time. Asa result of this, an entire insulator film 2 can be formed in such ashort time as shown in the following.

[0104] For instance, when the first insulator film SiON is formed withRLSA plasma under conditions of a pressure of 100 mTorr, gas flow ratesof Xe, N₂, H₂ and O₂ of 500 sccm, 25 sccm, 15 sccm and 1 sccm,respectively, and a temperature of 400° C., as shown in FIG. 9, a SiONfilm of a thickness of 1 nm can be deposited in approximately 30 sec.

[0105] However, it takes 245 sec to deposit SiON film of a thickness of3 nm under the same condition. The flow rate of O₂ of zero hardlyaffects the deposit rate. On the other hand, the CVD under conditions ofrespective flow rates of Xe, SiH₄ and N₂ gas of 500 sccm, 15 sccm and 20sccm, and a temperature of 400° C. accomplished the deposition rate ofapproximately 4.5 nm/min. Accordingly, a film thickness of 2 nm isdeposited within approximately 30 sec. As a result of this, in thepresent manufacturing method, within a total time of approximate 60 sec,an insulator film of a thickness of 3 nm can be deposited to result inremarkable improvement in the deposition rate compared with the directnitride method.

[0106] Further, variation of film thickness due to direct oxy-nitridedeposition with the above RLSA plasma, as shown in FIG. 10, is inproportion to time up to approximately 1 nm to reveal that a surfacereaction is the rate-determining step. However, when exceeding thisvalue, diffusion becomes rate-determining step to gradually slow thedeposition rate. Accordingly, in the present manufacturing method, SiONfilm of a thickness of 1 nm is formed by direct oxy-nitriding andthereafter SiN film is deposited by use of CVD method.

[0107] (Embodiment)

[0108] In the following, embodiment will be shown.

[0109] According to the present manufacturing method of semiconductors,on an n type silicon substrate in which device isolation is implemented,with an apparatus as shown in FIG. 2, with RLSA plasma, at a processingunit 32 shown in FIG. 2, a SiON film of 2 nm thickness is deposited. Thetotal thickness of the insulator film is 3 nm (in terms of oxide filmthickness). The SiON film is deposited under conditions of the flowrates of Xe/N₂/H₂/O₂=500 sccm/25 sccm/15 sccm/1 sccm, a pressure of 100mTorr, microwave output power of 2.0 kW, and a temperature of 400° C.

[0110] The CVD deposition is carried out under the conditions of theflow rates of Xe/SiH₄/N₂=500 sccm/15 sccm/20 sccm, a pressure of 100mTorr, microwave power of 25 kW and a temperature of 400° C. Thedeposition time is 62 sec. Under these conditions, throughput of 40pieces/hour is attained and practical applicability can be confirmed.

[0111] The uniformity of the film thickness also is excellent such as 3%in terms of 3σ.

[0112] Subsequently to the deposition of the gate insulator, p-typepolycrystalline Si gate is formed to evaluate a gate leakage current andinterface states. As the result of this, under an input electric fieldof 75 mV/cm, such excellent results as the gate leakage current of1.3×10⁻⁶ A/cm² and the interface states of 6.5×10¹⁰/cm²/eV can beobtained. Further, upon forming a p-MOSFET (L/W=0.25/10 μm) to measurean on state current, the value identical with or more than that of theoxide film (5.5×10⁻⁴ A/μm) can be obtained.

[0113] As shown in the above, according to the present method, excellentgate insulators of a thickness of approximately 3 nm can be formed withthe deposition rate compatible sufficiently with industrialapplicability.

[0114] According to the present invention, in an atmosphere of aprocessing gas, on an object to be processed consisting mainly ofsilicon, through a planar-array antenna having a plurality of slits,microwaves are irradiated. That is, by use of the method that usesso-called RLSA antenna, plasma is directly supplied on a siliconsubstrate to deposit SiN insulator films. Accordingly, the film qualityat the interface between the silicon substrate and the SiN insulatorfilm formed on the surface thereof can be successfully regulated.

[0115] In addition, according to another manufacturing method of thepresent invention, by use of the so-called RLSA antenna, a firstinsulator film is deposited, thereon a second insulator film isdeposited to result in a SiN film of excellent quality. In particular,when the second insulator film is deposited due to the CVD method, theinsulator film can be deposited in a short time. Accordingly, a SiN filmof high quality can be formed in a short time.

[0116] (A second mode of Implementation of the Invention)

[0117] Next, another example of a structure of semiconductor devicesproduced according to a method of the present invention, with an exampleof a semiconductor device provided with a gate insulator as an insulatorfilm, will be explained with reference to FIG. 1. In FIG. 1 A, referencenumeral 1 denotes a silicon substrate, reference numeral 11 a fieldoxide film, reference numeral 2 a gate insulator and reference numeral13 a gate electrode. The present invention is characterized in the gateinsulator 2. The gate insulator 2, as shown in FIG. 1B, is constitutedof a first film 21 of a thickness of for instance approximately 20angstroms and a second film 22 of a thickness of approximately 20angstroms. The first film 21 is formed at the interface with the siliconsubstrate 1 and consisting of an insulator film of excellent electricalproperty. The second film 22 is formed on an upper surface of the firstfilm 21 and consisting of an insulator film that is larger in depositionrate than that of the first film 21.

[0118] In this example, a first gas containing rare gas and nitrogen (N)and hydrogen (H) but not silicon (Si) and containing 50% or more and 99%or less of rare gas is converted into plasma. With this plasma, asurface of the silicon substrate 1 is converted to nitride to form afirst silicon nitride film (hereinafter refers to as “SiN film”). Thus,the first film 21 of excellent electrical property results. The secondfilm 22 larger in deposition rate than that of the first film 21 is asecond SiN film. The second SiN film is deposited by use of plasma thatis obtained by converting a gas containing rare gas and N and Si andcontaining rare gas of 50% or more and 99% or less to the plasma.

[0119] The multi-hole slot electrode 60 is constituted of a circularplate larger than the opening 51 in which lots of slots 60 a fortransmitting microwaves is concentrically formed. The length anddisposition spacing of the slots are determined according to wavelengthsof microwaves generated by a microwave power supply 61.

[0120] On the sidewall of the upper side of the vacuum chamber 50, forinstance at sixteen positions located equidistant apart along thecircumference direction thereof, gas supply tubes 72 are disposed. Fromthese gas supply tubes 72, a gas containing rare gas and N is uniformlydistributed in the neighborhood of the plasma area P of the vacuumchamber 50.

[0121] In the vacuum chamber 50, a susceptor 52 of a wafer W is disposedso as to face the gas supply chamber 54. The susceptor 52 is providedwith a built-in temperature regulator, thereby the susceptor 52 beingconstituted to work as a heat plate. In addition, to the bottom of thevacuum chamber 50 one end of the exhaust tube 53 is connected, the otherend of the exhaust tube 53 being connected to a vacuum pump 55.

[0122] Next, how to form an insulator film consisting of a gateinsulator 2 on a wafer W with the above apparatus will be explained.First, a gate valve that is disposed on the sidewall of the vacuumchamber 50 and not shown in the FIG. is opened. Thereafter, with atransporting arm that is not shown in the figure, the wafer W that isfor instance a silicon substrate 1 on the surface thereof a field oxidefilm 11 is formed is disposed on the susceptor 52.

[0123] Subsequently, the gate valve is closed to seal the insidethereof, thereafter with the vacuum pump 55 an inner atmosphere isevacuated through an exhaust tube 53 to be a prescribed degree of vacuumand to maintain there. On the other hand, microwaves of for instance2.45 GHz and 3 kW are generated by a microwave power supply 61. Themicrowaves are guided by a waveguide 63 through the multi-hole slotelectrode 60 and the gas supply chamber 54 into the vacuum chamber 50.Thereby, in the plasma area P at the upper side in the vacuum chamber50, plasma of high frequency is generated.

[0124] Here, the microwaves propagate in a square waveguide 63D insquare mode, are converted from the square mode to circular mode at acoaxial waveguide converter 63 c, propagate in the circular coaxialwaveguide 63B in circular mode, further propagate in a state expanded atthe circular waveguide 63A, are radiated from the multi-hole slot 60 aof the RLSA 60, and go through the gas supplying chamber 54 to be ledinto the vacuum chamber 50. At this time, due to use of the microwaves,higher density plasma can be generated, and due to radiation of themicrowaves from a lot of slots 60 a, the plasma becomes denser.

[0125] Then, while regulating the temperature of the susceptor 52 toheat the wafer W at for instance 400° C., Xe gas, N₂ gas and H₂ gas thatare the first gas are introduced from gas supplying tubes 72 at the flowrates of 500 sccm, 25 sccm, and 15 sccm, respectively, to implement thefirst step. In this step, the introduced gases are activated (beingconverted into plasma) by plasma flow generated in the vacuum chamber50, with the plasma, as shown in FIG. 7A, a surface of the siliconsubstrate 1 being converted to oxynitride to form a first insulator filmSiN 21. Thus, this nitriding process is implemented for 2 min forinstance to deposit the first SiN film 21 of a thickness of 20angstroms.

[0126] Then, microwaves of for instance 2.45 GHz and 200 W are guidedfrom the microwave power supply 61 to generate plasma in the vacuumchamber 3 and at the same time in a state of a temperature of forinstance 400° C. and a pressure of for instance 50 mTorr to 1 Torr, asecond gas is led into the vacuum chamber 3 to implement a second step.That is, from the gas supply chamber 54 a gas containing silicon forinstance such as SiH₄ gas is led at the flow rate of for instance 15sccm. At the same time, from the gas supply tubes 72, Xe gas, and N₂ gasare introduced at the flow rates of 500 sccm and 20 sccm, respectively.

[0127] In this step, the second gas that is introduced is converted intoplasma by the plasma flow generated at the vacuum chamber 50, therewithas shown in FIG. 7B, a second SiN film 22 is deposited on the first SiNfilm 21. The SiN film 22 being deposited with the deposition rate of forinstance 20 angstroms/min, the deposition process is implemented forinstance 1 min to form the second SiN film 22 of a thickness of 20angstroms. Thus, in a total time of 3 min, a gate insulator 2 of athickness of 40 angstroms can be formed. In the above first step, in theabove process deposition apparatus the plasma of high density isgenerated. Therewith, a first gas containing rare gas and N and H andnot Si and containing 50% or more and 99% or less of rare gas isconverted into plasma. Therewith, the surface of the silicon substrate 1heated at a temperature of for instance 300 to 400° C. is converted intonitride to form a first SiN film 21. Accordingly, the first SiN film 21of excellent electrical property can be obtained.

[0128] The electrical property of the insulator film is determined bythe number of defects, and the less the number of defects is, the morepreferable the electrical property is. The defect density of the firstSiN film 21 formed according to the above method is approximately7×10¹⁰/cm², which is less than approximately 1×10¹²/cm² of that ofthermal nitride film. Accordingly, it can be said that electricalproperty is excellent.

[0129] The reason why the electrical property of the first SiN film 21formed according to the above method is excellent as such is consideredas follows. First, the first gas contains rare gas and N and H and notSi, in which due to introduction of the rare gas, defects such asdensity of interface states are surmised to be suppressed in occurrence.In this case, as obvious from the experiment that will be describedlater, when the content of rare gas is less than 50%, the number ofdefects increases. When the content is 100%, the deposition can not beimplemented. By contrast, when 99% or less, though becoming smaller indeposition rate, deposition can be implemented without deteriorating thefilm quality. Accordingly, it is preferable to set at 50% or more and99% or less. In addition, due to introduction of a gas containing H, thedangling bonds can be decreased to result in suppression of occurrenceof defects. Accordingly, electrical property is considered to improve.

[0130] Further, when the first gas is converted into plasma by use ofthe plasma that is called such as ICP (Inductive Coupled Plasma), thenumber of defects of the obtained SiN film increases. The ICP isgenerated by supplying an electric field and magnetic field with a coilwound into a dome-like container shape to generate plasma from the firstgas. Therefrom, in the above plasma deposition apparatus, by generatingthe plasma of high density such as mentioned in the above to converttherewith the first gas into plasma, the electrical property isconsidered to improve.

[0131] In the above second step, in the above process depositionapparatus, high density plasma is generated and thereby the plasma ofthe second gas containing rare gas and N and Si is generated to depositthe second SiN film 22. Accordingly, the second SiN film 22 that islarger in deposition rate than that of the first SiN film 21 can beobtained.

[0132] The reason why such a large deposition rate can be attained isdue to introduction of a gas containing Si such as silane-based gas suchas SiH₄. By contrast, the simultaneous introduction of the rare gas isto lower the concentration of silane-based gas to avoid any difficultiesin regulation of film thickness due to a too fast deposition rate. Here,concerning the content of an inert gas, when contained too much, thedeposition rate becomes smaller, on the contrary when contained toolittle, the number of defects becomes larger. Accordingly, it ispreferable to set at 50% or more and 99% or less.

[0133] Further, in the above process, in depositing the second SiN film22, power of microwaves is lowered down to 200 W that is smaller thanthat (3 kW) employed for the first SiN film 21. This is due to thefollowing reason. Upon decomposition of SiH₄, the generated H₂ diffusesoutwards to lower the concentration of Si in the outward area relativeto that of the center area, resulting in less uniformity of the filmthickness of the SiN film 22. In order to prevent this from occurring,the power of microwaves is decreased to suppress excessive decompositionof SiH₄.

[0134] In addition, in the above process, the first and second steps areimplemented in the same plasma deposition apparatus. Accordingly, thefirst and second steps can be successively implemented to shorten thetotal deposition time, thereby the throughput being able to improve.Further, the above plasma processing apparatus being low in its electrontemperature, by depositing the first SiN film 21 and the second SiN film22 with this apparatus, the silicon substrate 1 is damaged less.

[0135] The second SiN film 22 formed according to the above method has adefect density of approximately 1×10¹¹/cm² to result in worse electricalproperties than that of the first SiN film 21. However, the portion thatis necessary to be good in electrical property is the portion where theSiN film contacts the silicon substrate, that is, an entire film is notnecessarily required to be electrically excellent. Accordingly, when thesecond SiN film 22 as such is deposited on the above layer than theinterface with the silicon substrate 1, the electrical property of thegate insulator 2 is not adversely affected.

[0136] Thus, in the above process, a gate insulator 2 is constituted ofa first SiN film 21 of excellent electrical property and a second SiNfilm 22 of which deposition rate is larger than that of the first SiNfilm 21. Accordingly, an insulator film of excellent electricalproperties can be obtained in a shorter deposition time.

[0137] To be specific, as in the above first process for instance, asilicon substrate 1 is processed to nitride with a first gas of Xegas/N₂ gas/H₂ gas=500 sccm/25 sccm/15 sccm. Then, as shown in FIG. 4,within the first 2 min, a SiN film of 2 nm (20 angstroms) can bedeposited. Thus, in the initial period of the processing, a largerdeposition rate can be obtained. However, when the film thicknessexceeds 2 nm, the deposition rate becomes smaller to take approximately20 min to deposit nitride film of 4 nm. On the contrary, as in theprocess of the second step, when a SiN film is formed by converting thesecond gas of SiH₄ gas/N₂ gas/Xe gas=15 sccm/20 sccm/500 sccm intoplasma, the deposition rate of 2 nm/min can be attained.

[0138] Accordingly, when a SiN film of a thickness of 4 nm is necessary,as shown in FIG. 12, first nitriding due to the first gas is carried outfor 2 min to form a first SiN film 21 of 2 nm at the interface with asilicon substrate 1. Thereafter, deposition due to the second gas isimplemented for 1 min on an upper surface of the first SiN film 22 toform a second SiN film 22 of a thickness of 2 nm. As a result of this, aSiN film of a thickness of 4 nm can be formed in 3 min.

[0139] The gate insulator 2 obtained thus by the above process ismeasured of capacitance and gate voltage. The electrical property shownin FIG. 13 is obtained. Even in the case of such a thin film thicknessas 4 nm, it is confirmed that electrical property identical with that ofthe existing SiO₂ film can be obtained.

[0140] Further, in the above plasma deposition apparatus, with, as thefirst gas, a gas in which Ar gas and N₂ gas and H₂ gas are mixed with aratio of 90:7:3 (Ar/N₂/H₂=450 sccm/35 sccm/15 sccm), under conditions ofa wafer temperature of 400° C. and a process pressure of 50 mTorr to 1Torr, microwave power of 2.45 GHz and 3 kW is introduced from themicrowave power supply 51 to implement the first step identical with theabove and to deposit a first SiN film 21 of a thickness of 20 angstroms.Then, with, as the second gas, a gas in which SiH₄ gas and N₂ gas and Argas are mixed with a ratio of 3:4:90 (SiH₄/N₂/Ar=15 sccm/20 sccm/450sccm), under conditions of a wafer temperature of 400° C. and a processpressure of 50 mTorr, microwave power of 2.45 GHz and 200 W is guidedfrom the microwave power supply to implement the second step and todeposit a second SiN film 23 of a thickness of 20 angstroms. The totaldeposition time is 4 min. The electrical property of the obtainedinsulator film is measured. Even in the case of such a thin filmthickness as 40 angstroms, it is confirmed to be electrically excellentand appropriate for a gate insulator.

[0141] Subsequently, an example of the experiment that was carried outto optimize a ratio of inert gas in a first gas will be explained. Inthis experiment, Xe gas and N₂ gas and H₂ gas are used as the first gas.In the above plasma deposition apparatus, under the conditions of awafer temperature of 400° C. and a process pressure of 50 mTorr to 1Torr, from a microwave power supply 51 microwaves of 2.45 GHz and 3 kWis guided to deposit a first SiN film 21 of a thickness of 20 angstroms.At this time, with the ratio of flow rates of N₂ gas and H₂ gas at 5:2,the content of Xe gas is varied in the range of from 30% and 99% todeposit the first SiN film 21. Thereafter, number of defects is measuredby use of CV measurement method. The electrical properties are evaluatedaccording to the numbers. The results are shown in FIG. 14. Theelectrical properties are evaluated in three grades of ◯ (good), X (bad)and Δ (intermediate).

[0142] As the results of this experiment, when Xe gas is contained inthe range of from 50% to 99%, the defect density is approximately7×10¹⁰/cm² and the electrical property is excellent. On the contrary,when the content of Xe gas is 40% or less, it is confirmed that thedefect density increases to result in deterioration of the electricalproperty.

[0143] In the above, the rare gas contained in the first gas can be,other than Xe, helium (He), neon (Ne) or krypton (Kr). As the first gas,a gas containing rare gas and NH₃ may be used. In addition, as thesecond gas, a gas containing rare gas and N and Si can be used. Here, asthe gas containing Si, other than SiH₄, Si₂H₆ may be used.

[0144] In the above plasma deposition apparatus, an example of employingmicrowaves of 2.45 GHz is explained. However, in the present invention,UHF of for instance 500 MHz can be used to generate the plasma. In thiscase, the slots of the multi-hole slot electrode are designed into longholes according to the frequency.

[0145] Next, another example of the present invention will be explained.In this example, the first insulator film 21 is composed of SiO₂ film.The SiO₂ film, for instance in the above plasma deposition apparatus,can be deposited by implementing plasma oxidation on the surface of thesilicon substrate 1. The plasma oxidation is implemented with the plasmaof the gas containing rare gas and oxygen (O) but not Si and containingthe rare gas in the range of 50% and more and 99% or less.

[0146] To be specific, as a gas that contains rare gas and O but not Siand contains the rare gas in the range of 50% or more and 99% or less, agas mixture of Ar gas and O₂ gas is used. These gases are introduced atthe flow rates of Ar gas/O₂ gas=500 sccm/15 sccm and under theconditions of a wafer temperature of 430° C. and a process pressure of50 mTorr to 1 Torr, from a microwave power supply, microwaves of 2.45GHz and 3 kW are introduced to convert Ar gas and O₂ gas into plasma.With this plasma, a surface of the silicon substrate 1 is oxidized fortwo min to form a SiO₂ film of a thickness of for instance 20 angstroms.On the obtained SiO₂ film, with the identical process with the above,the second SiN film 22 is deposited by for instance 20 angstroms to forman insulator film.

[0147] In this process, in a total time of 3 min for instance, aninsulator film of a thickness of 40 angstroms can be formed. The SiO₂film formed through plasma oxidation of silicon, being such low as7×10¹⁰/cm² in the defect density thereof, is excellent in electricalproperty. Here, the content of the inert gas is preferable to be in therange of 50% or more and 99% or less. It is because that when thecontent becomes smaller than 50%, density of interface states increases.

[0148] An insulator film is actually formed by use of the above processand the relationship between capacitance and gate voltage thereof ismeasured. The results are excellent to confirm being suitable as thegate insulator. It is understood that thereby, even when an insulatorfilm of such a thin total thickness as 40 angstroms is formed with SiO₂film as the first film 21, by depositing a second film 22 on the SiO₂film, a leakage current becomes smaller.

[0149] As the gas that contains rare gas and oxygen but not Si, acombination of rare gas and ozone (O₃) and a combination of rare gas andwater vapor (H₂O) may be used.

[0150] Next, still another example of the present invention will beexplained. In this example, a first film 21 of the insulator film isformed of a SiO₂ film formed through thermal oxidation of silicon. TheSiO₂ film can be formed due to rapid thermal oxidation process forinstance in which a silicon wafer is heated to approximately 850° C. andexposed to water vapor atmosphere.

[0151] Such a first film 21 is deposited by 20 angstroms in for instance5 min and thereon with the identical process with the above a second SiNfilm 22 is formed by for instance 20 angstroms to form an insulatorfilm. Thereby, in a total time of for instance 6 minutes the insulatorfilm of 40 angstroms can be formed. The SiO₂ film formed through thermaloxidation of silicon, being less in the defect density such as5×10¹⁰/cm², is excellent in electrical property. An insulator film isactually formed by the above process and relationship betweencapacitance and gate voltage is measured. The result is excellent and itis confirmed that the insulator film is suitable for the gate insulator.

[0152] Next, still another example of the present invention will beexplained. In this example, the first film 21 of the insulator film isformed of silicon oxynitride film, the silicon oxynitride film beingdeposited by annealing for instance SiO₂ film in an atmosphere of NO. Tobe specific, a silicon wafer having a silicon oxide layer of a thicknessof 20 angstroms is heated to a temperature of 850° C. and exposed to NOgas to form a thermal nitride film.

[0153] Due to this process, on the surface of the silicon substrate 1, asilicon oxynitride film of a thickness of for instance 20 angstroms isformed in 10 minutes. Thereon, as identical with the above process, asecond SiN film 22 of a thickness of for instance 20 angstroms isdeposited to form an insulator film of a thickness of 40 angstroms.

[0154] In this process, in a total time of for instance 11 minutes, aninsulator film can be formed. The silicon oxynitride film thus formedhas the defect density of approximately 5×10¹⁰/cm² and is excellent inelectrical properties. An insulator film is actually formed by the aboveprocess. Upon measuring the relationship between capacitance and gatevoltage thereof, it is found that the relationship is excellent and theinsulator film is suitable for the gate insulator.

[0155] As explained in the above, according to the present invention, aninsulator film is formed by depositing a first film of excellentelectrical property and a second film of fast deposition rate.Accordingly, an insulator film of excellent electrical property can beformed in a short time.

[0156] Although the present invention has been shown and described withrespect to a best mode embodiment thereof, it should be understood bythose skilled in the art that the foregoing and various other changes,omissions, and additions in the form and detail thereof may be madetherein without departing from the spirit and scope of the presentinvention.

What is claimed is:
 1. A manufacturing method of semiconductors,comprising the steps of: irradiating microwaves, in an atmosphere ofprocessing gas, on a substrate to be processed consisting mainly ofsilicon, through a planar-array antenna having a plurality of slits togenerate plasma containing oxygen, or nitrogen, or oxygen and nitrogen;and implementing with this plasma oxidizing, nitriding, or oxy-nitridingdirectly on a surface of the substrate to be processed to deposit aninsulator film of a thickness of 1 nm or less in terms of oxide film. 2.The manufacturing method of semiconductors as set forth in claim 1:wherein the processing gas contains N₂ or N₂O or NO or NH₃.
 3. Amanufacturing method of semiconductors, comprising the steps of:irradiating microwaves, in an atmosphere of processing gas, on asubstrate to be processed consisting mainly of silicon, through aplanar-array antenna having a plurality of slits to generate plasmacontaining oxygen, or nitrogen, or oxygen and nitrogen, and implementingwith this plasma oxidizing, nitriding, or oxy-nitriding directly on asurface of the substrate to be processed to deposit an insulator film ofa thickness of 1 nm or less in terms of oxide film; and depositing asecond insulator film on the first insulator film.
 4. The manufacturingmethod of semiconductors as set forth in claim 3: wherein the step offorming the second insulator film is a step of depositing an insulatorfilm consisting of silicon nitride.
 5. The manufacturing method ofsemiconductors as set forth in claim 3: wherein the step of depositingthe second insulator film is implemented by use of CVD method.
 6. Themanufacturing method of semiconductors as set forth in claim 3: whereinthe step of depositing the second insulator film is implemented by useof plasma irradiation.
 7. The manufacturing method of semiconductors asset forth in claim 6: wherein the step of depositing the secondinsulator film is a step of supplying plasma containing N₂ or NH₃ andmonosilane or dichlorosilane or trichlorosilane.
 8. The manufacturingmethod of semiconductors as set forth in claim 6: wherein the plasmairradiation is carried out through a planar-array antenna having aplurality of slits.
 9. A manufacturing apparatus of semiconductors forimplementing a manufacturing method of semiconductors of claim 1,comprising: a microwave power supply, a planar-array antenna having adevice for guiding the microwave and a plurality of slits, a temperaturerising unit for maintaining a temperature of a substrate to be processedat 400° C. or above, a gas supply unit for introducing a processing gasinto a reaction chamber, one or more of process chamber having anevacuating unit for decompressing a reaction chamber to 1 Torr or less,and a transporting unit for transporting in a vacuum the substrate to beprocessed.
 10. The manufacturing apparatus of semiconductors as setforth in claim 9: wherein two or more of the process chambers aredisposed so as to deposit gate insulators in parallel.
 11. Themanufacturing apparatus as set forth in claim 9: wherein a CVD chamberdifferent from the process chamber and a vacuum transportation unit arecomprised to deposit SiN due to CVD following direct oxy-nitriding. 12.A manufacturing method of semiconductor devices, comprising the stepsof: converting a gas containing rare gas and nitrogen and hydrogen orrare gas and ammonia but not silicon, and containing rare gas in therange of 50% or more and 99% or less into plasma to nitride with theplasma a surface of a silicon substrate to deposit a first siliconoxynitride film; and converting a gas containing rare gas and nitrogenand silicon, and containing rare gas in the range of 50% or more and 99%or less into plasma to deposit therewith on a surface of a first siliconnitride film a second silicon nitride film of larger deposition ratethan that of the first silicon nitride film.
 13. A manufacturing methodof semiconductor devices, comprising the steps of: converting a gascontaining rare gas and oxygen but not silicon, and containing rare gasin the range of 50% or more and 99% or less into plasma to oxidizetherewith a surface of a silicon substrate to deposit a silicon oxidefilm; and converting a gas containing rare gas and nitrogen and silicon,and containing rare gas in the range of 50% or more and 99% or less intoplasma to deposit therewith on a surface of the silicon oxide a siliconnitride film.
 14. A manufacturing method of semiconductor devices,comprising the steps of: oxidizing a surface of a silicon substrate todeposit a silicon oxide film; and converting a gas containing rare gasand nitrogen and silicon, and containing rare gas in the range of 50% ormore and 99% or less into plasma to deposit therewith on a surface of asilicon oxide film a silicon nitride film.
 15. A manufacturing method ofsemiconductor devices, comprising the steps of: depositing on a surfaceof a silicon substrate a silicon oxynitride film; and converting a gascontaining rare gas and nitrogen and silicon, and containing rare gas inthe range of 50% or more and 99% or less into plasma to deposittherewith on a surface of the silicon oxynitride film a silicon nitridefilm.
 16. The manufacturing method as set forth in claim 12, furthercomprising the step of: generating plasma with high frequency power of300 MHz or more and 2500 MHz or less to convert therewith a gas intoplasma.